New silver and trityl salts of large, exceptionally inert, weakly coordinating carborane anions are reported. The anions include the 10-vertex carborane closo-CB9H10-, 1, its pentabrominated derivative closo-6,7,8,9, 10-Br5CB9H5-, 2, the 12-vertex hexabrominated derivative closo-7,8,9,10,11,12-Br6CB11H6, 3, the cobalt(III) bis(dicarbolli(le) ion Co(1,2-C2B9H11)(2)(-), 4, and its hexabrominated derivative Co(8,9,12-Br-3- 1,2-C2B9H8)2-, 5. X-ray structures have been determined for Ag[l] and Ag(al-toluene)[2]. Halide abstraction reactions with these silver salts have been explored with respect to the labile complex IrCl(CO)(PPh(3))(2). Ag[2] forms an Ir --> Ag metal-metal-bonded adduct rather than undergoing metathesis. The adduct has been characterized by X-ray crystallography and shows eta(3) bonding to Ag+ via bromine atoms from the Br5CB9H5- anion. The more coordinating anion 4 leads unexpectedly to [Ir(CO)(PPh(3))(3)][4] from IrCl(CO)(PPh(3))(2) and [Fe(eta(5)-Cp)(eta(6)-p-xylene)][4] from Fe(Cp)(CO)(2)I, both of which have been characterized by X-ray crystallography. This work shows that the gain in stability arising from bromination of carborane anions does not occur at the expense of increased coordinating ability, despite the addition of lone pairs. Rather, bromination leads to decreased nucleophilicity. This unexpected result has been confirmed by ranking anions Y- in order of their increasing carbonyl stretching frequencies in compounds of the type FeCp(CO)(2)Y. This shows that Br6CB11H6-, 3, is the least coordinating anion in the series, substantially less than SbF6-. The size, solubility, inertness, and low nucleophilicity of this and related carborane anions suggest wide and varied applications throughout organic and inorganic metathesis and cation chemistry.